The optical transport network (OTN), standardized by the International Telecommunication Union Telecommunication Standardization Sector (ITU-T), is used in long distance large capacity network.
An optical transport unit (OTU) signal as a main signal of OTN has a nest structure of layer. In the nest structure, an OTUk layer is arranged on the outermost side, followed by an ODUk-tandem connection monitoring (TCM) layer, and an ODUk-path monitoring (PM) as described in ITU-T G.709. In a channelized structure, the outermost layer is followed by an ODUj-TCM layer and ODUj-PM layer.
A redundancy structure is incorporated in OTN in case of a defect in an apparatus or a transmission path (a disconnection of an optical fiber). The incorporation of redundancy is standardized as subnetwork connection (SNC) protection in Standard ITU-T G. 873.1 (July 2011).
FIG. 5 and FIG. 6 illustrate OTN. FIG. 5 is Figure II-3 in ITU-T G.798.1 (January 2013). A functional model is illustrated in the left-hand portion of FIG. 5, and an implementation model is illustrated in the right-hand portion of FIG. 5. FIG. 6 is Figure II-4 in ITU-T G.798.1 (January 2013). A functional model is illustrated in the left-hand portion of FIG. 6, and an implementation model is illustrated in the right-hand portion of FIG. 6.
In the SNC protection, HO ODUk SNC/S in FIG. 5 and HO ODUk SNC/I in FIG. 6 are configured so that a lower layer having the redundancy structure is switched if a defect is detected in the termination of the higher layer of the nest structure.
Related technique is disclosed in ITU-T G.798 (January 2013) Appendix II.